Terminal insulator



R. C. WALDRON TERMINAL INSULATOR Oct. 15,1935.

Filed April 11, 1932 IAIIVENTOR am/15.

Patented Oct. 15, 1935 PATENT OFFICE TERMNAL INSULATOB Richard 0.Waldron. Clifton, N. 1., assignor to The Okonlte Company, Passaio, N.1., a corporation of New Jersey -Application April 11, 1932, Serial No.604,442

' 4 Claims. (01. 173-353) My invention relates to the provision of aterminal insulator of improved construction and particularly adaptedforuse in connection with the installation of rubber insulated cables.

Rubber insulated cables for high voltages require some arrangement .toprevent flashover circuit.

It is common practice to install potheads on the cable. These areusually oirporcelain for insulating purposes fitted with a base and thenecessary terminal fittings. The cable is placed inside the pothead andthe pothead filled with an insulating compound to prevent electricalfailure. From an operating standpoint these potheads are satisfactorybut their cost and the labor of installing is often excessive and tosome extent prohibitive. As a matter of fact in short length cables suchas from a generator to outdoor switches or/transformers the cost of suchpotheads for terminating the cable may be as high as the entire cost ofthe cable itself.

.The present invention provides an improved. type of insulator adaptedto be used in place of potheads in which the required safety fromflashovers is maintained.

In. the .accompanying drawing I have shown different embodiments of myinvention.

Fig. l is a.part sectional elevational view of a single conductor cablewith my improved structure applied thereto:

Pig. 2 is a similar view of a mo my invention; while v Fig. ,3 is a partsectional elevational view of a difled form or I terminal insulatorhaving a higher flashover value than the form shown in Fig. 1, forinstance.

Referring to the drawing in detail and first the outside of the cable.Inasmuch as the insulation 2 of the cable and the material of theinsulator 4 are compressible there will be perfect 5 contact between theinsulation 2 and the insulator when the insulator is forced into place.

.To exclude air and to obtain a permanent bond cement is applied tothese surfaces before they are fitted together and to still furtherincrease the electrical strength of this path insulatingtape shown at 5is applied about the 'cable at the top and bottom of the insulator 4.

If voltage is now applied between the lug} and the sheath 2' ofthe'cable, which as usual 5 is grounded, the only leakage paths arealong the surface of the insulator 4 or between the insulator and theoriginal insulation 2.

By a'construction such as above described the strength of the latterpath may be made greater than the air leakage path along the surface ofthe insulation 2. This leakage path is increased by ribs 8 on the bottomof the insulator 4 so that the leakage path along the bottom or undersurvface of the insulator to the grounded sheath 2- 5 is stronger thanthe flashover through the air. whereby in the event of breakdown thedischarge follows a path remote from the lower surface of the insulator.It is evident that this flashover value may be varied by controlling theMaw sions of the insulator.

For outdoor use the wet flashover values such as would be obtainedduring a. rainstorm must be considered and in my invention the flashoveris maintained high by the ribs 6 above described.

A comparison of the flashover values obtained with my insulator and witha plain cable end with no insulator will be of interest.

Flaabover 40 in K. v.

Wet Dry 4s 85 46 is so 2s 40 as u 40 so The above table shows the savingin the leak- 50 age distance which maybe obtained by the use of myinsulator.

After the cables have been in service for some time the flashover forthe plain cables would decrease duetothecollection of dirt while the .inthe same fashion as described in connection with Fig. 1, the hole 9being slightly smaller than the outside of the cable to which the deviceis to be applied.

The flashover voltage may be increased by using a glazed surface for theouter shell but in order'to form a satisfactory seal over the cable endthe center portion must be elastic. The shell I may be cut thick asshown or may be very thin and the elastic center 8 may be molded intothe shell or the shell may be applied to the previously manufacturedcenter 8 as by paint ing.

In Fig.3 I have shown a construction in which two insulators 4 areemployed, these insulators being of the same construction as describedin connection with Fig. 1. This plurality of insulators is employed forincreasing the flashover value of the installation and two or even moreinsulators may be employed on a single cable if desired. I

It will be seen from theforegoing that my invention provides aninsulator for terminal cables wherein the cable is insulated with acompressible composition. in which the insulator has a center ofcompressible composition or it may be of compressible compositionthroughout, the hole in the insulator which permits of the insulatorbeing applied to the cable being of smaller diameter than the outside-ofthe cable so as to snugly fit the same and perfect contact is providedby reason of this fact and by reason of the fact that the insulation andthe insulator are of elastic material.

WhatIclaimis-- 1. In combination a high voltage power cable comprising acompressible-rubber insulated single conductor having a terminal at oneend and a grounded means spaced from said terminal end, a protectivemeans comprising a terminal insulator having a bore therethroughreceiving the insulation of the conductor, the inside diameter ofsaid'bore before assembly being smaller than the outside diameter of therubber insulation of the conductor, thereby eliminating air pockets andreducing electrical leakage along the area of contact between the cableinsulation and the bore of the insulator by maintaining intimate contactbetween the rubber insulation of the cable and the-insulator, theleakage path along the under surface of the insulator to said groundedsurface of the insulator.'

2. In combination a high voltage power cable comprising a singleconductor and an outer covering ofcompressible-rubber insulatingmaterial for the conductor, s'aid cable having a terminal at one end andgrounded means spaced from said terminal end, a protective meanscomprising a terminal insulator having a bore therethrough receiving theconductor insulation, the walls of, the bore in the insulator being ofthe same coinpressible-rubber insulating material as the said outercovering of the cable and stretched over the insulation of the cableconductor so as to be under compression thereby eliminating air pocketsand reducing electrical leakage along the area of contact between thecable insulation and the walls of the bore of the insulator bymaintalningintimate contactbetween the rubber insulation of the cable.and the rubber walls of the insulator bore, theleakage path along theunder surface of the insulator to said grounded means being strongerthan the flashover through the air,

whereby in the event of breakdown the discharge follows a path remotefrom the lower surfaceof.

the insulator. 3. In combination a high voltage power cable comprising asingle conductor insulated with-.1 compressible-rubber insulation andhaving a tertaining'intimate contact between the cable insulation andthe walls of the insulator bore, cement for bonding the insulator andthe insulating covering of the cable, insulating tape about the.insulation of the cable and the sides of the insulator forming anadditional dielectric to prevent electrical leakage along the area ofcontact between the cable insulation and the insulator bore, the leakagepath along theunder surface of the insulator .to said grounded meansbeing stronger than the flashover through the air. whereby in the eventof breakdown the discharge follows a path remote from the lower surfaceof the insulator.

4. In combination a high voltage power cable comprising'a singleconductor, compressible-rubber insulation for the conductor, said cablehaving a terminal at one end and grounded means spaced from saidterminal end, a protective means comprising a terminal insulator of thesame material as the said cable insulation and having a boretherethrough receiving the conductor insulation, said insulator beingstretched over the insulating material of the cable, thereby tomaintainintimate contact between the insulator and the insulation of theconductor, cement for bonding the insulator and the insulating coveringof the cable and for excluding gas and air from between the insulatorand the cable insulation received by the insulator, the leakage pathalong the under surface of the insulator to said grounded means beingstronger than the flashover. through the air, whereby in the event ofbreakdown the discharge follows a path remote from the lower surface ofthe insulator.-

RICHARD o. wannnou. 1o

